Pressure-sensitive carbonless transfer sheet and method for providing a chemically formed image on an untreated substrate

ABSTRACT

An encapsulated liquid reactant precursor and a co-reactant therefor are supported on the under surface of a donor sheet that is placed over an untreated surface (i.e, devoid of reactant precursor and co-reactant) of a receptor sheet or other substrate. Upon pressure-effected rupture of the capsules, a substantial amount of both the reactant precursor and the coreactant physically transfers to the untreated surface to provide, as a chemical reaction product, an essentially smudgefree, eradication-resistant, right-readable image on the untreated receptor surface. This donor transfer sheet and method are especially desirable where the receptor to be imaged is a data processing card or record on which a reactant and/or coreactant coating could adversely affect processability through data processing equipment; or the receptor to be imaged has a rigid non-flat surface on which a conventional carbonless receptor coating is impractical; or where only a small area of the receptor is to be imaged.

United States Patent 1191 Jablonski et al.

[4 1 Dec. 24, 1974 1 PRESSURE-SENSITIVE'CARBONLESS TRANSFER SHEET AND METHOD FOR PROVIDING A CHEMICALLY FORMED IMAGE ON AN UNTREATED SUBSTRATE [75] Inventors: Richard B. Jablonski, Lambertville,

N.J.; James F. Martone, Lexington, Ky.

[73] Assignee: International Business Machine Corporation, Armonk, NY.

22 Filed: Apr. 16, 1973 21 Appl. No.: 351,710

[52] U.S C1. l17/36.8, 117/369 [51] Int. Cl B4lm 5/00 [58] Field Of Search 117/362, 36.1, 36.8, 36.9

[56] References Cited I UNITED STATES PATENTS 2,711,375 6/1955 Sandberg 117/362 2,872,863 2/1959 Newman et al 117/362 X 2,932,582 4/1960 Pesa et a1 l17/36.2 3,020,171 2/1962 Bakan et al 117/362 3,088,028 4/1963 Newman 117/361 X 3,287,154 11/1966 Haas 117/369 3,305,382 2/1967 Orinik 117/364 X l/197l Phillips 117/362 3,697,323 10/1972 Brown et a]. 117/362 X Primary Examiner-Thomas J. Herbert, Jr. Attorney, Agent, or Firm-Henry E. Otto, Jr.

[57] ABSTRACT An encapsulated liquid reactant precursor and a coreactant therefor are supported on the under surface of a donor sheet that is placed over an untreated surface (i.e, devoid of reactant precursor and coreactant) of a receptor sheet or other substrate. Upon pressure-effected rupture of the capsules, a substantial amount of both the reactant precursor and the coreactant physically transfers to the untreated surface to provide, as a chemical reaction product, an essentially smudge-free, eradication-resistant, rightreadable image on the untreated receptor surface. This donor transfer sheet and method are especially desirable where the receptor to be imaged is a data processing card or record on which a reactant and/or co-reactant coating could adversely affect processability through data processing equipment; or the receptor to be imaged has a rigid non-flat surface on which a conventional carbonless receptor coating is impractical; or where only a small area of the receptor is to be imaged.

11 Claims, 2 Drawing Figures AFTER IMAGING PATENTED 3. 856,554

BEFORE IMAGING AFTER IMAGING PRESSURE-SENSITIVE CARBONLESS TRANSFER SHEET AND METHOD FOR PROVIDING A CHEMICALLY FORMED IMAGE ON AN UNTREATED SUBSTRATE CROSS-REFERENCE TO RELATED APPLICATION US. patent application of Richard B. Jablonski et al., Ser. No. 275,394, filed July 26, 1972, entitled Pressure Sensitive Recording System and Method of Providing a Split Image Therefor, assigned to the assignee of the present invention.

BACKGROUND OF THE INVENTION This invention relates to pressure-sensitive transfer sheets and methods, and more particularly to an improved transfer sheet of the so-called carbonless type which supports an encapsulated liquid reactant and a co-reactant therefor that, upon rupture of the capsules by application of localized pressure, are adapted to physically transfer to an untreated surface of a substrate to provide a visible, chemical reaction product image on said untreated surface.

Numerous carbonless systems have heretofore been proposed involving encapsulated liquid dyes or reactants that, upon rupture of the capsules, create an image by release or physical transfer of the colored dye or by chemical reaction of the encapsulated reactant with a co-reactant on the same or an adjacent surface.

. But, insofar as is known, in all previous self-contained systems (i.e., those with both the reactant and coreactant on the same surface), no imaging occurred on any adjacent untreated surface that was devoid of both reactant and co-reactant. In prior art self-contained systems employing an encapsulated reactant and a coreactant, the application of localized pressure effected merely a chemical reaction product image on the reactant/co-reactant supporting surface.

The only known prior art system in which an image might be produced on an untreated surface is one wherein one of two superposed sheets is coated with an encapsulated colored marking fluid or colored dye; but in such systems, the images are formed not by any chemical reaction, but by capsule rupture and physical transfer of colored ink or dye to the untreated sheet. But systems employing colored inks or dyes have several disadvantages. For example, the capsule supporting sheet must be heavily pigmented to obscure the highly colored imaging matter. Moreover, if such inks and dyes are capable of penetrating the receptor sheet, they will also be subject to continuing migration and dissolution.

SUMMARY OF THE INVENTION Applicants have discovered that certain non-obvious advantages over prior art arrangements are achieved by providing a pressure-sensitive donor sheet supporting on one surface thereof both an encapsulated reactant in solution and a distinctive co-reactant therefor, preferably in the form of separate coatings. When the coated surface of the donor sheet is placed face down in contact with an untreated surface of a receptor sheet or substrate and the capsules are ruptured by localized application of pressure, a substantial amount of both the reactant and co-reactant physically transfer to the untreated surface and there react to produce an essentially smudge-free, chemical reaction product image.

The term untreated surface, as used herein, means a surface that is devoid of both reactant and co-reactant.

Applicants pressure-sensitive carbonless transfer sheet is especially useful in applications where it is undesirable or impractical to have a reactant and/or coreactant coating preapplied to the sheet on which the image is desired; e.g., tabulating cards or the like on which a chemical coating could adversely affect the ability to process the cards through data processing equipment, or articles on which the surface to be imaged is only' a small fraction of the total surface of the article or is irregular in configuration. Thus, no chemically reactive coating need be preapplied to the surface to be imaged that would or might change the properties or characteristics of the said surface; and when imaged, the card has a dry, smudge-free chemical reaction product image that does not impair its machine processing ability. With applicants formulations hereinbelow set forth, a visible mirror image of the image formed on the untreated receptor sheet is provided on the reactant/co-reactant coated surface of the donor sheet; this is useful as a security feature on legal documents, checks, etc. to produce automatically on the coated back of the document a mirror image of the right reading image imprinted on the uncoated face of the document and any alteration ofwhich mirror image can be readily detected.

Other objects and advantages of the invention will become apparent from the following more detailed description and from the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING FIGS. 1 and 2 are elevational sectional views, to greatly enlarged scale, of a pressure-sensitive donor sheet embodying the invention and supporting encapsulated reactant and co-reactant coatings for physical transfer to and chemical reaction on the adjacent untreated surface of a receptor sheet. FIG. 1 denotes the condition before and FIG. 2 the condition after the transfer of reactant and co-reactant from the donor sheet to the receptor sheet.

DESCRIPTION OF PREFERRED EMBODIMENT According to the invention, sheet 10 is adapted to be placed with its co-reactant coating; 12 face down in intimate physical contact with the untreated somewhat absorptive surface 14 of a receptor substrate, such as a tabulating card or sheet 15. By a stylus, imprint member, or the like that exertsat least a preselected magnitude of impact or shear force, sufficient localized pressure is applied to the composite of sheets 10 and 14 to rupture the capsules 13. When these capsules rupture,

the reactant solution will be released; and this solution,

together with a substantial amount of the co-reactant in coating 12, will physically transfer from donor sheet I0 to the untreated surface 14 of sheet 15. The reactant solution and co-reactant thus transferred to sheet 15 chemically react to immediately produce in untreated surface 14 a dry, right-reading, permanent image 16 corresponding to the right-reading image pattern of pressure applied to the upper surface of sheet 10.

According to a feature of the invention, the receptor surface 14 is somewhat absorptive so that image 16 is actually absorbed into the surface; i.e., it is formed substantially within the receptor surface rather than applied on it, as would be the case if the image were formed solely by physical transfer of a transfer medium. This makes the image 16 essentially erasure and alteration resistant, as well as smear and smudge free.

A sufficient proportion of the released reactant solution and co-reactant will generally remain on sheet to chemically react in situ to produce simultaneously on the underside of donor sheet 10 a dry reaction product mirror image 17 of the image 16 produced on sheet 15. In most instances, this mirror image will be an incidential product of the main chemical reaction that produces the right-reading image 16 on the untreated sur face 14. However, in certain applications the creation of such a mirror image may be useful or desirable as a security feature, in that there will be recorded on the underside of sheet 10 a mirror image 17 of the rightreading image 18 imparted on the upper side of sheet 10. This chemically formed mirror image 17 is embedded in the underside of sheet 10, rendering it essentially impossible to alter without such attempted alteration being readily detectable. Thus, if image 17 is not a mirror image of the right-reading image 18, the observer will be alerted to the fact that image 18 has been altered. This would be highly desirable for legal documents, such as last wills and testaments. It is also useful where checks or drafts are computer-prepared by running through a highspeed printer as continuous forms, and a print-out record carbonless copy is made of the indicia entered on the check; in such case, when image 18 is imprinted on the face of the check, applicants coatings 11,12 on the back of the check would concurrently form the security mirror image 17 and image 16 on the permanent record ply. Coatings 11, 12 may be applied to the entire back surface; or, if desired, to only a restricted area.

The pressure-rupturable capsules 13 must be formed of a film forming material that has the requisite properties, including sufficient strength to preclude inadvertent rupture. While many materials might be satisfactory, aldehyde condensation polymers, especially urea formaldehyde condensation polymers, are especially suitable. The capsules are preferably from about 1 to 50 microns in size and formed in any suitable manner already known in the art; e.g., in the manner described in U.S. Pat. Nos. 2,730,457; 3,432,327; 3,5l6,846 or 3,558,341. The capsules contain a liquid reactant precursor; preferably this is in the form of a solution comprising a chemically reactive dye precursor dissolved in an appropriate solvent. A particularly suitable class of reactant precursors are dithiooxamide and its N,N-disubstituted derivatives; of these, the N,N-diorganosubstituted-dithiooxamides, dissolved in organic solvents, are preferred. It will be understood that the solution will preferably contain one or more additional ingredients for specialized purposes such as enhancing storage stability. speed and/or intensity of colorproducing reaction, etc.

Applicants improvement resides, primarily, in providing a reactant coating 11 and a co-reactant coating 12 that will physically transfer to an untreated somewhat absorptive surface 14 of a tabulating card 15 or the like, and there chemically react to promptly produce a dry, eradication-resistant image of commercially acceptable intensity and durability that will not impede processing of the card through data processing machines. The combination of chemical reaction and solubility characteristics and absorption characteristics into the cardstock assures that a substantial part of the coreactant coating will transfer with the reactant solution and be absorbed; the remainder of the coating and solution will remain in situ and provide a security feature for applications, such as of the type above described.

The reactant coating 11 and co-reactant coating 12 are preferably applied by a conventional coating apparatus before a paper web is severed into sheets 10. Coating 11 is preferably applied, then dried as the web moves in line to a second coating apparatus that applies the coating 12. However, it will be apparent that, if preferred, the coatings 11, 12 may be applied as a composite single coating, rather than sequentially as just described.

Now that the general nature of the invention has been described, the following examples are presented as illustrative of the encapsulated reactants and the coreactants that have been used sucessfully in applicants pressure-sensitive carbonless transfer sheet and recording system and method.

EXAMPLES l4- ln each of the following tabulated examples l4, a

200 CB (Coated Back) sheet of Action" paper marketed by Minnesota Mining and Manufacturing Company was used to constitute the donor substrate 10 and encapsulated reactant coating 11. While the'specific formulation of said coating has not been disclosed by said company, the capsules 13 forming part thereof are known to contain dithiooxamide or one of its N,N'- di-substituted derivatives dissolved in an organic solvent, as taught in U.S. Pat. No. 3,481,759. Based upon a cursory analysis, the capsules are believed to contain solvents of tributyl phosphate and diethyl phthalate and reactive components of N,N-bis(2-octanoyloxyethyl) dithiooxamide coated with a binder containing azinccarboxylate; and the capsule walls are formed of urea formaldehyde resin.

The co-reactant coatings 12 were prepared by adding the ingredients specified in Table I to a suitable solvent, such as denatured alcohol. Each mixture was then shaken for 15 minutes by a vibratory paint shaker using steel ballswithin the container to facilitate solution and dispersion. The resulting solution was then applied as a coating over the encapsulated reactant coating 11 and dried to remove the solvent.

The variously coated sheets 10 were then placed, with the co-reactant-coated surface face down, in inti mate physical contact with the untreated surface 14 of tabulating card 15. The cards 15 were then imaged by applying localized pressure to the upper uncoated surface of the sheets 10 using well known techniques such as ball-point pens, pencils, typewriter keys, and imprinting devices employing embossed credit cards.

Table I expresses the formulations of the co-reactant coatings 12 of Examples 1 through 4 in terms of percentage by weight of the various ingredients less the volatile solvent which ultimately evaporates. The examples are listed in order of preference; i.e., Example l is preferred. An evaluation of these formulations with respect to image intensity, image development speed and appearance of the coated sheet after imaging are also included in Table l, with the letters E, G, F, P

applicants unique ingredient transfer and chemical reaction. The sodium benzoate is not essential, but is be lieved to contribute to image intensity on the receptor sheet 15.

signifying, respectively, Excellent, Good, Fair and 5 The formulations above listed in Examples 1-4 do Poor. not constitute all of the formulations prepared and TABLE I Examples Ingredients in '7? by Weight of Dry Coatings Ingredients No. 1 No.2 No. 3 No. 4

Nickel (11) chloride hexahydrate 20.5 15.0 20,0 25.0 *Sodium ricinoleate 20.5 35.0 46.2 31.3 Lithium stearate 10.2 16.7 12.5 *Stearic acid 20.5 25.0 27.6 18.7 Sodium benzoate 10.3 6.3 Anti-oxidant alkylated 7.7 8.3 6.2 6.2

polyhydroxy phenol (Santovar A, Monsanto Chemical Co.) Zinc resinate 10.3 Solvent denatured alcohol (preferably PM 3163, Ashland Chemical Co.)

Evaluation Applied By No. 1 No. 2 No. 3 No. 4

Ultimate image z lmprinter G F F E Intensity Ball Point Pen E G G G Image Developmet Speed Donor Sheet Aesthetic G G Appearance Shelf Life G Essential for reaction alcohol at to concentratlon.

The formulations of these Examples provided a visible image 17 on the donor sheet 10 of sufficient intensity to be useful for security feature applications.

In the preferred formulation (Example 1), the image develops usable intensity more rapidly than that of Example 2, and donor sheet appearance is better. Both exhibit good temperature and environment stability (i.e., shelf life) and produce on card 15, by ingredient transfer and reaction, chemically formed images of commercially acceptable intensity.

In the above formulations, it was found that the various ingredients serve the following functions: The nickel (II) chloride provides the metal cation that ultimately complexes with dithiooxamide and/or its derivatives. The sodium ricinoleate provides the anion that combines with the nickel (ll) chloride to form (in part) nickel ricinoleate which is highly soluble in the solvent systemincluded in the capsule fill of the 3M CB sheet. The lithium stearate and stearic acid facilitate release of the imaging materials from the donor sheet. The Santovar A antioxidant confers long term environmental stability to the coating. In one formulation, the amount of sodium ricinoleate is reduced and zinc resinate substituted; in this instance, the zinc resinate pro vides a substance that reacts with the nickel (II) chloride to form (in part) nickel resinate which is highly soluble in the solvent system included in the capsule fill ofthe 3M CB sheet, and it also binds the coating to the substrate and provides coating cohesion.

The ingredients just specified are important to assure 25 45 total but always more stearic acid Nickel (11] chloride hexahydrate Sodium ricinoleate Lithium stearate Stearic acid Antioxidant (e.g., Santovar A) Zinc resinate Sodium benzoate Although, as illustrated, the coated donor sheet 10 is described as imaging an untreated surface 14 of a tabulating card 15, it should be noted that donor sheets having the compositions above described have also been used successfully to image untreated signature panels on credit cards, untreated paper sheets (e.g., bank checks, labels) and painted or coated objects. It is contemplated that, if desired, the donor sheet 10 might also be used to image porous or nonporous receptors which serve as intermediaries from which the image is transferred to another surface.

It should be noted that the split-image" formulations disclosed in the above-identified related application were tested in reactive transfer applications (i.e., imaging an untreated surface), but found to be totally unsuitable.

From the foregoing, it will be seen that applicants have demonstrated that a dry, right-readable, eradication resistant, smudge free, chemical reaction product image 16 can be provided on an untreated surface 14 of a receptor sheet, card or the like by a pressureeffected physical transfer of reactant and co-reactant from a donor sheet to said receptor sheet, the image resulting from the chemical reaction which occurs on and in the untreated surface. With most formulations,

mirror image 17 of the indicia 18 imprinted on the top side of the donor sheet 10 will be formed by chemical reaction on the underside of said donor sheet, this being highly desirable for security feature applications of the type above described.

While the invention has been particularly shown and described with reference to a preferred embodiment thereof, it will be apparent that the foregoing and other changes may be made in the donor sheet, and in the specified formulations and method without departing from the spirit, scope and teaching of the present invention. Accordingly, the sheet, system and method herein disclosed are to be considered merely as illustrative, and the scope of the invention is to be limited only as specified in the claims.

,What is claimed is:

l. A pressure-sensitive carbonless transfer sheet having a surface supporting a multitude of microscopic pressure-rup'turable capsules containing a reactant solution comprising a precursor taken from the class of dithiooxa'mide and its N,N'di-substituted derivatives, and a solvent and also supporting a co-reactant for the reactant solution, which co-reactant comprises nickel (ll) chloride, sodium ricinoleate and stearic acid,

the reactant solution and co-reactant being adapted,

upon application of a localized pressure to the sheet and consequently rupture of the capsules while said surfaceis in intimate contact with another surface devoid of reactant and co-reactant, to cause a substantial portion of the co-reactant and reactant solution to physically transfer to said other surface to cause chemical reactions to occur between the precursor and co-reactant for rapidly providing a dry, chemically formed image on such other surface.

2. A sheet according to claim 1, wherein upon application of such localized pressure to another surface of the sheet opposite the first-mentioned surface, the remainder of the co -reactant and reactant solution will remain in situ and chemically react to provide on the first-mentioned surface a chemically formed mirror image of the image formed by application of pressure to such other surface.

3. A sheet according to claim 1, wherein the coreactant comprises, by weight, when dried, about 10 30 percent nickel (ll) chloride; -50 percent sodium ricinoleate; 2545 percent stearic acid and lithium stearate as a combined total, but for any percentage selected there being ore stearic acid by weight than lithium stearate; and 2 10 percent anti-oxidant.

4. A sheet according to claim 1, wherein the co reactant consists by weight, when dried, of essentially about 21 percent nickel (ll) chloride; 21 percent sodium ricinoleate; 10 percent lithium stearate; 20 percent stearic acid; 10 percent sodium benzoate; 10 percent zinc resinate; and 8 percent anti-oxidant.

5. A sheet according to claim 1, wherein the coreactant consists by weight, when dried, of essentially about 15 percent nickel (11) chloride; 35 percent sodium ricinoleate; 17 percent lithium stearate; 25 percent stearic acid; and 8 percent anti-oxidant.

6. A sheet according to claim 1, wherein the coreactant consists by weight, when dried, of essentially about 20 percent nickel (ll) chloride; 46 percent sodium ricinoleate; 28 percent stearic acid; and 6 percent anti-oxidant.

7. A sheet according to claim 1, wherein the coreactant consists by weight, when dried, of essentially about 25 percent nickel (l1) chloride; 31 percent sodium ricinoleate; 13 percent lithium stearate; 19 per cent stearic acid; 6 percent sodium benzoate; and 6 percent anti-oxidant.

8. In a pressure-sensitive recording system, the combination of one member having a substantially flat surface supporting a multitude of microscopic pressurerupturable capsules containing a reactant solution comprising a precursor taken from the class of dithiooxamide and its N,N'di-substituted derivatives, and the co-reactant comprises nickel (II) chloride, sodium ricinoleate and stearic acid, and another member having a somewhat absorptive surface which is devoid of reactant and co-reactant,

the reactant solution and co-reactant being adapted, upon application of a localized pressure to said members and consequent rupture of the capsules while said surfaces are superimposed in intimate contact, to cause at least some of the reactant solution to partly dissolve at least some of the coreactant and physically transfer from the flat surface to the absorptive surface and be absorbed therein sufficiently to cause the chemical reaction that occurs between precursor and co-reactant to provide in the absorptive surface a chemically formed image that is immediately dry and essentially smudge-free and erasure resistant.

9. The system according to claim 8, wherein said members are flat sheets that are superimposed with said flat surface in face-down contact with said absorptive surface to cause the image formed in said absorptive surface to correspond identically to the pattern of applied localized pressure when such pressure is applied to a surface of said one member opposite said flat surface.

10. The system according to claim 8, wherein the 10- calized pressure is applied to said members by imprinting a right-readable image on a different surface of said one member opposite the fiat surface, and the reactant solution and co-reactant react chemically to provide on said flat surface a mirror image of the right-readable image, the mirror image being provided concurrently with and as a part of the same chemical reaction that provides the image in the absorptive surface, the image in the absorptive surface being right readable.

11. A system according to claim 8, wherein the coreactant comprises, by weight, when dried, about 10-30 percent nickel (ll) chloride; 15-50 percent sodium ricinoleate; 2545 percent stearic acid and lithium stearate with a preponderance of stearic acid; and

2-10 percent anti-oxidant. 

1. A PRESSURE-SENSITIVE CARBONLESS TRANSFER SHEET HAVING A SURFACE SUPPORTING A MULTITUDE OF MICROSCOPIC PRESSURERUPTURABLE CAPSULES CONTAINING A REACTANT SOLUTION COMPRISING A PRECURSOR TAKEN FROM THE CLASS OF DITHIOOXAMIDE AND ITS N,N''DI-SUBSTITUTED DERIVATIVES, AND A SOLVENT AND ALSO SUPPORTING A CO-REACTANT FOR THE REACTANT SOLUTION, WHICH CO-REACTANT COMPRISES NICKEL (II) CHLORIDE, SODIUM RICINOLEATE AND STEARIC ACID, THE REACTANT SOLUTION AND CO-REACTANT BEING ADAPTED, UPON APPLICATION OF A LOCALIZED PRESSURE TO THE SHEET AND CONSEQUENTLY RUPTURE OF THE CAPSULES WHILE SAID SURFACE IS IN INTIMATE CONTACT WITH ANOTHER SURFACE DEVOID OF REACTANT AND CO-REACTANT, TO CAUSE A SUBSTANTIALLY PORTION OF THE CO-REACTANT AND REACTANT SOLUTION TO PHYSILCALLY TRANSFER TO SAID OTHER SURFACE TO CAUSE CHEMICAL REACTIONS TO OCCURS BETWEEN THE PRECURSOR AND CO-REACTANT FOR RAPIDLY PROVIDING A DRY, CHEMICALLY FORMED IMAGE ON SUCH OTHER SURFACE.
 2. A sheet according to claim 1, wherein upon application of such localized pressure to another surface of the sheet opposite the first-mentioned surface, the remainder of the co-reactant and reactant solution will remain in situ and chemically react to provide on the first-mentioned surface a chemically formed mirror image of the image formed by application of pressure to such other surface.
 3. A sheet according to claim 1, wherein the co-reactant comprises, by weight, when dried, about 10 - 30 percent nickel (II) chloride; 15-50 percent sodium ricinoleate; 25-45 percent stearic acid and lithium stearate as a combined total, but for any percentage selected there being more stearic acid by weight than lithium stearate; and 2 - 10 percent anti-oxidant.
 4. A sheet according to claim 1, wherein the co-reactant consists by weight, when dried, of essentially about 21 percent nickel (II) chlorIde; 21 percent sodium ricinoleate; 10 percent lithium stearate; 20 percent stearic acid; 10 percent sodium benzoate; 10 percent zinc resinate; and 8 percent anti-oxidant.
 5. A sheet according to claim 1, wherein the co-reactant consists by weight, when dried, of essentially about 15 percent nickel (II) chloride; 35 percent sodium ricinoleate; 17 percent lithium stearate; 25 percent stearic acid; and 8 percent anti-oxidant.
 6. A sheet according to claim 1, wherein the co-reactant consists by weight, when dried, of essentially about 20 percent nickel (II) chloride; 46 percent sodium ricinoleate; 28 percent stearic acid; and 6 percent anti-oxidant.
 7. A sheet according to claim 1, wherein the co-reactant consists by weight, when dried, of essentially about 25 percent nickel (II) chloride; 31 percent sodium ricinoleate; 13 percent lithium stearate; 19 percent stearic acid; 6 percent sodium benzoate; and 6 percent anti-oxidant.
 8. In a pressure-sensitive recording system, the combination of one member having a substantially flat surface supporting a multitude of microscopic pressure-rupturable capsules containing a reactant solution comprising a precursor taken from the class of dithiooxamide and its N,N''di-substituted derivatives, and the co-reactant comprises nickel (II) chloride, sodium ricinoleate and stearic acid, and another member having a somewhat absorptive surface which is devoid of reactant and co-reactant, the reactant solution and co-reactant being adapted, upon application of a localized pressure to said members and consequent rupture of the capsules while said surfaces are superimposed in intimate contact, to cause at least some of the reactant solution to partly dissolve at least some of the co-reactant and physically transfer from the flat surface to the absorptive surface and be absorbed therein sufficiently to cause the chemical reaction that occurs between precursor and co-reactant to provide in the absorptive surface a chemically formed image that is immediately dry and essentially smudge-free and erasure resistant.
 9. The system according to claim 8, wherein said members are flat sheets that are superimposed with said flat surface in face-down contact with said absorptive surface to cause the image formed in said absorptive surface to correspond identically to the pattern of applied localized pressure when such pressure is applied to a surface of said one member opposite said flat surface.
 10. The system according to claim 8, wherein the localized pressure is applied to said members by imprinting a right-readable image on a different surface of said one member opposite the flat surface, and the reactant solution and co-reactant react chemically to provide on said flat surface a mirror image of the right-readable image, the mirror image being provided concurrently with and as a part of the same chemical reaction that provides the image in the absorptive surface, the image in the absorptive surface being right readable.
 11. A system according to claim 8, wherein the co-reactant comprises, by weight, when dried, about 10-30 percent nickel (II) chloride; 15-50 percent sodium ricinoleate; 25-45 percent stearic acid and lithium stearate with a preponderance of stearic acid; and 2-10 percent anti-oxidant. 